Slaves key expire is orchestrated by the master. Sometimes the master
will send the synthesized DEL to expire keys on the slave with a non
trivial delay (when the key is not accessed, only the incremental expiry
algorithm will expire it in background).
During that time, a key is logically expired, but slaves still return
the key if you GET (or whatever) it. This is a bad behavior.
However we can't simply trust the slave view of the key, since we need
the master to be able to send write commands to update the slave data
set, and DELs should only happen when the key is expired in the master
in order to ensure consistency.
However 99.99% of the issues with this behavior is when a client which
is not a master sends a read only command. In this case we are safe and
can consider the key as non existing.
This commit does a few changes in order to make this sane:
1. lookupKeyRead() is modified in order to return NULL if the above
conditions are met.
2. Calls to lookupKeyRead() in commands actually writing to the data set
are repliaced with calls to lookupKeyWrite().
There are redundand checks, so for example, if in "2" something was
overlooked, we should be still safe, since anyway, when the master
writes the behavior is to don't care about what expireIfneeded()
returns.
This commit is related to #1768, #1770, #2131.
I guess the initial goal of the initialization was to suppress GCC
warning, but if we have to initialize, we can do it with the base-case
value instead of NULL which is never retained.
in the case (all chars of the string s found in 'cset' ),
line[573] will no more do the same thing line[572] did.
this will be more faster especially in the case that the string s is very long and all chars of string s found in 'cset'
Track bandwidth used by clients and replication (but diskless
replication is not tracked since the actual transfer happens in the
child process).
This includes a refactoring that makes tracking new instantaneous
metrics simpler.
PFCOUNT is technically speaking a write command, since the cached value
of the HLL is exposed in the data structure (design error, mea culpa), and
can be modified by PFCOUNT.
However if we flag PFCOUNT as "w", read only slaves can't execute the
command, which is a problem since there are environments where slaves
are used to scale PFCOUNT reads.
Nor it is possible to just prevent PFCOUNT to modify the data structure
in slaves, since without the cache we lose too much efficiency.
So while this commit allows slaves to create a temporary inconsistency
(the strings representing the HLLs in the master and slave can be
different in certain moments) it is actually harmless.
In the long run this should be probably fixed by turning the HLL into a
more opaque representation, for example by storing the cached value in
the part of the string which is not exposed (this should be possible
with SDS strings).
start_server now uses return value from Tcl exec to get the server pid,
however this introduces errors that depend from timing: a lot of the
testing code base assumed the server to be actually up and running when
server_start returns.
So the old code that waits to see the pid in the log file was restored.
